trajto

Two senses, and they are worth keeping apart. A trajto of a person is a characteristic, something in the character: lia plej bona trajto. The trajtoj of a face are its features, the lines of it, which is the older and more literal reading of a word that means "a drawn line". Karaktero is the whole disposition; a trajto is one strand of it.

Trajto and trajno are not related in any way you can use. Both are borrowed roots that happen to begin traj-, and neither contains a piece the other does. Very far back they do share the Latin trahere, "to draw", since a train is a thing drawn along and a trait is a line drawn, but that is etymology for its own sake: in Esperanto they are two unanalysable roots and knowing one tells you nothing about the other.